In order to provide a proper seal, it has been thought that it is necessary to have a seal on the top surface of the container as well as on the outer cylindrical surface of the finish or neck of the container. Thus, in compression mold liners a satisfactory seal has been provided as shown in, for example, U.S. Pat. Nos. 4,378,893, 4,407,422 and 4,418,828 incorporated herein by reference. In these patents, the closure is provided with an annular lip spaced from the base wall and defining an annular channel or recess and a plastic sealing liner is compression molded such that it is held in position by integral liner-engaging projections on the base wall and the annular lip to form a liner that has an annular sealing bead that engages the outer side wall surface of the container. In another type of plastic beverage closure shown in U.S. Pat. Nos. 4,462,502 and 4,658,976, a circular flexible resilient liner is provided which is rotatable relative to the closure and has a diameter greater than the outside diameter of the container lip. An annular projection is provided at the juncture of the base wall and skirt of the closure and preferably has a configuration when viewed in cross-section which has a horizontal portion, a vertical and a convex portion connecting the horizontal and vertical portion one to the other providing for sealing along an outer cylindrical side surface of the edge of the finish of the container. In each of the aforementioned constructions, the construction relies on the flexing of the base wall of the closure to enhance the side seal on the cylindrical surface of the container finish.
In U.S. Pat. Nos. 5,265,747 and 462,187, there is disclosed a plastic beverage closure comprising a base wall, a peripheral skirt and a plurality of threads on the inner surface of the skirt for engagement with the threads of a container which may be made of glass or plastic. The plastic closure includes a compression molded seal extending about the periphery of the inner surface of the base wall and the juncture of the base wall to the peripheral skirt. The closure includes a central axially thickened portion; a channel surrounding the thickened portion and extending radially to an annular radially thickened portion on the skirt at the juncture with the base wall. A concave surface extends from the base of the channel and merges with the surface of the annular portion. A compression molded liner is provided on the thickened portion, channel and concave surface of the closure and defines a planar sealing surface for contact with the end surface of the finish of the container and an arcuate surface for engaging the arcuate surface of a container. In another form, the inner surface of the end wall has a uniform thickness and the planar surface and the annular liner receiving surfaces are coplanar. In another form, the skirt of the closure has a radially thickened portion on its inner surface along which a portion of the liner extends.
In closures for use with oil, a closure has been used wherein the closure has a base wall with a peripheral skirt with internal threads and the base wall is planar with a uniformly thick compression molded liner thereon. The liner engages a flat upper surface of the finish and the inner edge of the finish but is not in engagement with the outer surface or the outer edge of the finish.
The above described closures have liners which are compression molded onto the closures. In the process of compression molding, a molten plastic pellet is delivered into the interior of the closure and liner forming tooling is introduced into the interior of the closure and shut off at the area into which the liner is to be formed from the remaining areas of the closure including the threads. If the shut off of the area is not achieved, molten plastic material can flash into the thread area of the closure or the liner material may be not uniformly formed in the closure, for example, creating an overfill on one side and a void on the opposite side of the closure. In such instances, the plastic closure must be scrapped.
Among the objectives of the present invention are to provide a plastic closure and a method of making the closure wherein the plastic closure has a configuration such that the plastic closure will provide an effective seal on glass and plastic containers while at the same time providing a positive shut off; wherein there is a more uniform flow of the liner material during compression molding thereby eliminating flash or voids; which can be used as a vacuum closure for containers filled with hot contents; which can be used as a closure for containers filled with non-carbonated cold liquids; and which can be used for containers containing carbonated liquids.
In accordance with the invention, the plastic closure is for a container which has a finish with a top surface portion, a cylindrical outer surface portion, and a curved portion at the juncture of the top surface portion and the outer surface portion. The closure includes a base wall, a peripheral skirt having an inner surface and threads on the inner surface of the skirt for engaging the container. The base wall has an inner planar surface and a compression molded liner is compression molded and bonded on the planar surface of the plastic closure. The liner has a periphery spaced radially inwardly of the peripheral skirt and the threads on the skirt. The peripheral portion of the liner has an outer annular inclined surface. The inclined surface tapers radially inwardly away from the base wall of the closure and is positioned for engaging the top surface portion of the finish and the inner surface of the container and out of engagement with the outer surface of the finish of the container. The plastic closure is made by forming a closure with a base wall having an inner planar surface and compression molding a liner on the planar surface of the plastic closure. The step of compression molding the liner is such as to form the liner with a periphery spaced radially inwardly of the peripheral skirt and the threads on the skirt as well as the outer surface of the finish. The step of forming the liner includes forming the peripheral portion of the liner such that it has an outer surface being positioned for engaging the top surface portion of the finish and the inner edge of the container and being out of engagement with the outer surface of the container.